1. Field of the Invention
The present invention relates to a control valve, used for a variable capacity type compressor constituting a refrigerant circulating circuit of a vehicle air conditioner to compress refrigerant gas and also to a variable capacity compressor having such a control valve.
2. Description of the Related Art
As this type of variable capacity compressor, for example, a swash plate type variable capacity type compressor is known and is shown in FIG. 9. In the variable capacity type compressor, which will be simply referred to as a compressor in this specification hereinafter, when the swash plate 101 is rotated, the pistons 102 are reciprocated, so that refrigerant gas is compressed, and the discharge capacity can be adjusted when the pressure in the crank chamber 103 is adjusted. In this case, the swash plate 101 is driven by an engine of a vehicle, which is an external drive source.
In order to adjust the pressure in the crank chamber 103, there are provided an extraction gas passage 105 having a fixed restriction 105a connecting the crank chamber 103 to the suction chamber 104, a supply passage 107 connecting the discharge chamber 106 to the crank chamber 103, and an electromagnetic control valve 108 arranged in the supply passage 107. When the degree of opening of the control valve 108 is adjusted, the quantity of high pressure gas supplied from the discharge chamber 106 into the crank chamber 103 via the supply passage 107 is controlled with respect to the quantity of gas extracted from the crank chamber 103 into the suction chamber 104 via the extraction passage 105, so that the pressure in the crank chamber 103 can be determined. According to the change in the pressure in the crank chamber 103, a difference between the pressure in the crank chamber 103 and the pressure in the cylinder bores 109 on either side of the piston 102 is changed, so that the inclination angle of the swash plate 101 can be changed. According to the change in the inclination angle of the swash plate 101, the stroke of the pistons 102 is adjusted, that is, the discharge capacity of the compressor can be adjusted.
For example, when the pressure in the crank chamber 103 is raised and a difference between the pressure in the crank chamber 103 and the pressure in the cylinder bores 109 is increased, the inclination angle of the swash plate 101 is decreased, so that the discharge capacity of the compressor is decreased. In the drawing, the swash plate 101 shown by a solid line is located at the minimum inclination angle. On the contrary, when the pressure in the crank chamber 103 is lowered and a difference of between the pressure in the crank chamber 103 and the pressure in the cylinder bores 109 is decreased, the inclination angle of the swash plate 101 is increased, so that the discharge capacity of the compressor is increased. In the drawing, the swash plate 101 shown by a two-dotted chain line is located at the maximum inclination angle.
However, a problem may arise in that, when the air conditioner having the compressor of the above structure, for example, is started at midday or in the afternoon in summer, substantially simultaneously with the start of a vehicle engine, the air conditioning operation should be started immediately according to the demand of an operator, but there is a case in which it takes several tens of seconds to actually start the effective air conditioning operation. The reason why it takes several ten seconds to start the effective air conditioning operation is that the change of the operating condition of the compressor from the minimum discharge capacity state is delayed and it takes time for the compressor to reach the maximum discharge capacity state. The reason why the change of the operating condition from of the compressor the minimum discharge capacity state is delayed is that a large quantity of liquid refrigerant, which stays in the crank chamber 103 during the stoppage of the engine, is agitated and evaporated by the heat generated at the start of the compressor and the rotation of the swash plate 101, and therefore, refrigerant gas cannot be sufficiently extracted from the crank chamber 103 in a short period of time, and the pressure in the crank chamber 103 is kept high. That is, the swash plate 101 is held at the minimum inclination angle irrespective of the adjustment of the degree of opening of the supply passage 107 conducted by the control valve 108 until evaporation of liquid refrigerant in the crank chamber 103 is completed.
The reason why a large quantity of liquid refrigerant stays in the crank chamber 103 during the stoppage of the engine as described above is because of a difference between the thermal capacity of the compressor and that of the condenser 111 or the evaporator 112 in the external refrigerant circuit. That is, the condenser 111 and the evaporator 112, which are heat exchangers, are easily influenced by the change in the temperature in the surroundings, but, the compressor, the thermal capacity of which is large and the surface area of which is small, is less influenced by the change in the temperature in the surroundings. Accordingly, as the temperature of the outside air rises from the morning to the noon, the temperature of the condenser 111 and the evaporator 112, which are easily influenced by the temperature change, is quickly raised and the temperature of the compressor, which is less influenced by the temperature change, is slowly raised, so condensation of refrigerant gas begins in the compressor due to the difference between the temperature of the condenser 111 and the evaporator 112 and the temperature of the compressor. When condensation of refrigerant gas begins in the compressor, the volume of refrigerant is reduced due to the transfer from the gaseous state to the liquid state, and the pressure in the compressor is reduced, so that a flow of refrigerant gas directly from the condenser 111 and the evaporator 112 into the compressor occurs. Refrigerant gas flowing from the condenser 111 and the evaporator 112 into the compressor is condensed and the flow of refrigerant gas into the compressor and the condensation of refrigerant gas in the compressor are repeated. At midday or in the afternoon when the rise of temperature of the outside air is substantially settled and the difference between the temperature of the compressor and the temperature of the condenser 111 and the evaporator 112 becomes smaller, the quantity of liquid refrigerant in the compressor (crank chamber 103) becomes a maximum.
In order to solve the above problems, the following three countermeasures can be considered.
The first countermeasure is that the minimum inclination angle of the swash plate 101 is set to a greater value. By doing so, even if the compressor is in the minimum discharge capacity state, a certain flow rate of refrigerant can be ensured in the refrigerant circulating circuit. Accordingly, even if the change of the operating condition of the compressor from the minimum discharge capacity state is hindered when liquid refrigerant is in the crank chamber 103 as described above, the compressor can suck and discharge a certain amount of refrigerant, so the suction pressure is quickly lowered and refrigerant is quickly extracted from the crank chamber 103, and the operating condition of the compressor can be changed from the minimum discharge capacity state in a short period of time. However, when an absolute value of the minimum discharge capacity is made higher, the compressor can not cope with a state in which the load of air conditioning is low, and in the case where a power transmission mechanism having a clutch between the compressor and the vehicle engine is adopted, it becomes necessary to turn the clutch on and off frequently.
Also, in the case where a clutchless type power transmission mechanism is adopted, the compressor is driven at all times while the engine is being operated. Therefore, when the refrigerating air conditioning is not needed, the discharge capacity of the compressor is minimized so that the load torque can be reduced in order to reduce a power loss of the engine as small as possible. Therefore, if the minimum inclination angle of the swash plate 101 is set to a greater value, it is impossible to reduce the load torque of the compressor when the refrigerating air conditioning is not needed, and the load on the engine is increased.
The second countermeasure is that the diameter of the fixed restriction 105a of the extraction passage 105 is increased, that is, the amount of restriction is reduced. When the amount of restriction of the fixed restriction 105a is reduced, the refrigerant extracting capacity of the extraction passage 105 is enhanced, and when the compressor is set in motion, liquid refrigerant in the crank chamber 103 can be quickly made to flow into the suction chamber 104. In this case, liquid refrigerant in the crank chamber 103 is made to flow into the suction chamber 104 in the form of gas or liquid. Therefore, pressure in the crank chamber 103 can be quickly reduced and the discharge capacity can be increased.
However, the supply passage 107, the crank chamber 103 and the extraction passage 105, in a sense, constitute a leakage route with respect to the compressed refrigerant gas. Accordingly, the arrangement in which the amount of restriction of the fixed restriction 105a of the extraction passage 105 is set small means that a quantity of leakage of compressed refrigerant gas is increased when the discharge capacity is changed, and the efficiency of the compressor is deteriorated. When the amount of restriction of the fixed restriction 105a of the extraction passage 105 is set small, a rise in pressure in the crank chamber 103 is slowly conducted. Therefore, the capacity control property is deteriorated, especially when the discharge capacity is changed to a smaller capacity side.
The third countermeasure is that the control valve is composed of a three-way valve, and the degrees of opening of both the extraction passage 105 and the supply passage 107 are adjusted by one control valve. However, in the structure of the three-way valve, a valve element for adjusting the degree of opening of the extraction passage 105 and a valve element for adjusting the degree of opening of the supply passage 107 are integrated in one body, and therefore, it is difficult to conduct such a complicated motion by the three-way valve that the degree of opening of one of the passages 105 and 107 is kept constant and the degree of opening of the other of the passages 105 and 107 is changed.
In order to solve the problems caused in the above three countermeasures, the following two methods can be considered. One is a method in which the fixed restriction 105a of the extraction passage 105 is changed into an electromagnetic type variable restriction so that the amount of restriction of the variable restriction can be reduced only when the compressor is set in motion. The other is a method in which a second extraction passage is provided along with the extraction passage 105, and an electromagnetic valve is arranged in the second extraction passage, so that the electromagnetic valve is opened only in the case of starting the compressor. That is, a control valve different from the control valve 108 provided in the supply passage 107 is arranged in the extraction passage. However, this method is disadvantageous in that it is necessary to provide another electromagnetic valve in addition to the control valve 108 and the manufacturing cost is increased and, further, space to install the electromagnetic valves is required.
The present invention has been accomplished to solve the above problems caused in the prior art. It is an object of the present invention to provide a compact control valve capable of adjusting the degrees of opening of the first and second fluid passages composing a fluid circuit, with a low manufacturing cost. Also, it is an object of the present invention to provide a compact variable capacity type compressor provided with the above control valve.
A control valve, according to the present invention, comprises a valve housing having first and second fluid passages, independently movable first and second plungers arranged in the valve housing, a magnetic flux generating device generating a magnetic flux according to a supplied electric power to provide electromagnetic attraction force acting on and between the first and second plungers, a first valve element connected to the first plunger for adjusting the degree of opening of the first fluid passage, and a second valve element connected to the second plunger for adjusting the degree of opening of the second fluid passage.
In this arrangement, both plungers are movable and respectively connected to the valve elements. Accordingly, the degrees of opening of two fluid passages can be adjusted by one electromagnetic structure (two iron cores and one magnetic flux generating means are combined). Accordingly, the present invention can provide a structure of adjusting the degrees of opening of the fluid passages at low cost and further a space in which the structure is arranged can be reduced, compared with the conventional structure in which it is necessary to provide two electromagnetic structures for adjusting the degrees of opening of two fluid passages. Therefore, the cost and size of the variable capacity compressor can be reduced.
Preferably, a pressure sensitive structure is provided for giving a load to at least one of the first and the second valve elements according to a fluid pressure or a fluid pressure difference in the fluid circuit.
In this arrangement, the fluid pressure or a fluid pressure difference in the fluid circuit is reflected in the adjustment of the degrees of opening of the fluid passage, so it is not necessary to provide an electric structure for detecting the fluid pressure or a fluid pressure difference and also it is not necessary to provide a complicated program for controlling the magnetic flux generating means.
Preferably, a first urging means urging the first plunger away from the second plunger, and a second urging means for separating the second plunger away from the first plunger are further provided, wherein the urging force of the first urging means is different from the urging force of the second urging means, so that the start of movement of the first plunger toward the second plunger against the urging force of the first urging means occurs separately from the start of the movement of the second plunger toward the first plunger against the urging force of the second urging means according to the magnetic attraction force.
In this arrangement, the electromagnetic attraction force to start the movement of the first plunger is made different from the electromagnetic attraction force to start the movement of the second plunger, so it is possible to give the control valve such a characteristics the degree of opening of one of the fluid passages is kept constant and only the degree of opening of the other of the fluid passages is adjusted.
Preferably, the urging force of the first urging means is lower than the urging force of the second urging means, and the control valve includes a first plunger movement restricting means for restricting a movement of the first plunger to approach the second plunger, and according to an increase in the electromagnetic force, the first plunger first moves toward the second plunger to a position restricted by the first plunger movement restricting means against the urging force of the first urging means, and the second plunger then moves toward the first plunger against the urging force of the second urging means.
In this arrangement, when the electromagnetic attraction force is changed in a low range, the degree of opening of the second fluid passage is kept constant, and only the degree of opening of the first fluid passage is adjusted by the first valve element. When the electromagnetic attraction force is changed in a high range, the degree of opening of the first fluid passage is kept constant, and only the degree of opening of the second fluid passage is adjusted by the second valve element.
Preferably, the first and second plungers are coaxially arranged, and the magnetic flux generating means surround the first and second plungers.
The present invention also provides a variable capacity type compressor having a control valve which has an identical feature to the above described one.
In this compressor, preferably, the first fluid passage connects the control chamber to a suction pressure region or a discharge pressure region in the refrigerant circulating circuit, and the second fluid passage connects the control chamber to the suction pressure region or the discharge pressure region, and the discharge capacity can be changed by adjusting the pressure in the control chamber when the degrees of opening of the first and second fluid passages are adjusted by the control valve.
Preferably, one of the first and second fluid passages connects the control chamber to the discharge pressure region, and the other of the first and second fluid passages connects the control chamber to the suction pressure region.
In this arrangement, the most common structure of controlling the discharge capacity is embodied. Both the inlet side control and the outlet side control are conducted by the control valve. The inlet side control is conducted as follows; when the discharge capacity is controlled, the pressure in the control chamber is adjusted by positively adjusting the supply of the high pressure gas from the discharge pressure region. The outlet side control is conducted as follows; when the discharge capacity is controlled, the pressure in the control chamber is adjusted by positively adjusting the extraction of gas into the suction pressure region. Accordingly, compared with a case in which the discharge capacity control is conducted only by one of the inlet side control and the outlet side control, the capacity control property can be enhanced.
Preferably, the control valve includes a pressure sensitive structure for giving a load to at least one of the first and the second valve elements according to refrigerant pressure in the refrigerant circulating circuit or according to a difference of refrigerant pressure.
Preferably, the pressure sensitive structure is composed in such a manner that the degree of opening of the fluid passage is adjusted by at least one of the first and second valve elements so that refrigerant pressure in the refrigerant circulating circuit, which is set by the electromagnetic attraction force, or a difference in the refrigerant pressure, can be maintained.
Preferably, the pressure sensitive structure is composed in such a manner that a load caused by the refrigerant pressure in the suction pressure region is given to at least one of the first and the second valve bodies.
Preferably, the pressure sensitive structure is composed in such a manner that a load caused by a difference between the refrigerant pressure at the first pressure monitoring point and the refrigerant pressure at the second pressure monitoring point, which is set on the downstream side or the lower pressure side of the first pressure monitoring point in the refrigerant circulating circuit, is given to at least one of the first and the second valve bodies.
In this arrangement, as long as the electromagnetic attraction force is not changed, the pressure sensitive structure autonomously adjusts the degree of opening of the fluid passage according to an actually detected fluid pressure or a difference in the fluid pressure so that a constant fluid pressure or a constant difference in the fluid pressure can be maintained. When the electromagnetic attraction force is changed by the control conducted from the outside, setting values of the fluid pressure or the difference in the fluid pressure, which are references of the motion of the pressure sensitive structure, are changed. Therefore, the pressure sensitive structure is operated according to the actual fluid pressure or the difference in the fluid pressure so that these new setting values can be accomplished.